This invention relates generally to a system for improved utilization of a gaseous hydrocarbon fuel when stored in pressurized vessels aboard internal combustion engine vehicles and more particularly to a utilization system whereby the gaseous hydrocarbon fuel is first sorbed in storage vessels employing sorptive materials and thereafter more effectively recovered therefrom for use during vehicle operation.
The development and use of various gaseous hydrocarbon fuels to supply the motive power for internal combustion engine vehicles has been underway for a considerable time period. A greater interest is developing in such use of gaseous hydrocarbon fuels including natural gas, methane, propane, butane and the like, to replace conventional liquid petroleum vehicle fuels such as gasoline or diesel fuel by reason of dwindling reserves for the liquid petroleum fuels as well as adverse effects of vehicle emissions when liquid petroleum fuels are employed. The already developed vehicle utilization systems employing an on-board and self-contained supply of such gaseous hydrocarbon fuels store the fuel under pressure in one of two general ways. In a very high pressure utilization system, the gaseous fuel is stored on-board at pressures in the approximate range 2000-3000 psi which requires quite expensive storage vessels and refueling equipment. It has also been previously found that a use of on-board fuel storage vessels containing sorptive materials permits storage of such fuels at relatively low pressures up to approximately 600 psi. In accordance therewith, various types sorptive materials such as zeolites, activated carbon and silicon gels have been utilized to increase the storage capacity of on-board vehicle systems employing such gaseous hydrocarbon fuels. While it has also been previously found that these gaseous hydrocarbons can be stored on-board the vehicles in a liquid state at or near atmospheric pressure, such liquified gas storage is reported to require comparatively expensive cryogenic equipment both on-board the vehicle and in the refueling system.
In U.S. Pat. No. 4,522,159 there is disclosed a utilization system for gaseous hydrocarbon fuel powered vehicles which stores the fuel on-board at relatively low pressures up to approximately 500 psig using sorptive storage means. The disclosed vehicle utilization system comprises means for on-board storage of a self-contained supply of the gaseous hydrocarbon fuel, a prime mover, means for conveying the gaseous hydrocarbon fuel to and from the on-board storing means and means for controlling the pressure of the gaseous hydrocarbon fuel from the on-board storing means to the prime mover. The on-board storing means is said to include one or more vessels or cylinders, containing a predetermined sorbent material for allowing a given amount of the gaseous hydrocarbon fuel to be stored at such lower pressure. The prime mover such as an internal combustion engine includes means for combining the gaseous hydrocarbon fuel with air to produce the mechanical energy therefrom necessary to move the vehicle. The conveying means is reported to be adapted so as to convey the gaseous hydrocarbon fuel to the on-board storing means from a stationary refueling apparatus, and also to convey the gaseous hydrocarbon fuel from the on-board storing means to the combining means of the prime mover during operation of the vehicle. In the preferred embodiment, the maximum pressure at which the gaseous hydrocarbon fuel is stored in the on-board storing means is the range of approximately 100 psig to approximately 400 psig. As furthermore particularly disclosed therein, the preferred embodiment provides the desorbed fuel in a separate manner to the engine carburetor means for combination thereat with an air supply.
A similar type low-pressure system for the utilization of a gaseous hydrocarbon to power automotive type vehicles is also disclosed in U.S. Pat. No. 4,523,548. Multiple cylinders are employed containing either adsorbent or absorbent material including molecular sieves, activated carbon zeolite compounds, various clays and silicate gel which store the hydrocarbon gas at pressures ranging from approximately 100 psig to approximately 400 psig. The gas is filtered before storage with sorptive filtering means to remove undesirable constituents such as odorant additives (dimethylsulfide and the like) which are frequently included in natural gas as a safety measure. The reported purpose (column 14, lines 19-22) for removing such constituents is further said to be maximizing the capability of the storage vessels to sorb the lighter hydrocarbons such as methane. A still different storage system for gaseous hydrocarbon fuels is disclosed in U.S. Pat. No. 4,817,684. An illustrated mixture of methane containing an additive such as dimethylsulfide, tetrahydrothiothene (THT), tertiary butyl mercaptan (TBM) and others is adsorbed at elevated pressures within the storage vessel containing a bed of solid adsorbent particles which has been preconditioned at a lower pressure with the additive. Storage of the gas mixture within the storage vessel is said to proceed in accordance with isothermal curves depicted in FIG. 2 of said prior art reference (column 5, lines 26-32).
In all of the above referenced prior art types sorptive utilization systems, a considerable amount of the sorbed gas will be left on the solid sorptive medium (contained in the cylinder or other type storage vessel) after the depletion at atmospheric pressure is reached. As high as fifty (50%) percent of the sorbed gas contained in the storage vessel at charge can be retained in the sorption bed at depletion depending upon the particular sorbable gas and solid sorption medium being employed. The sorbed gas left after depletion is not usable in any normal storage application since it will require a vacuum application to remove it. Accordingly, there still remains a serious need for better means to desorb more of the stored gas at atmospheric conditions of pressure and temperature.
It is therefore an object of the present invention to provide more effective means of utilizing the stored fuel of an on-board gaseous hydrocarbon fuel powered vehicle system.
It is another object of the present invention to increase the capacity of an on-board gaseous hydrocarbon fuel powered vehicle system by recovering more of the stored fuel.
It is a still further object of the present invention to provide more effective means for the operation of a gaseous hydrocarbon powered vehicle system having the gaseous hydrocarbon fuel stored on-board under pressure in a suitable sorptive medium so that more of the stored fuel becomes available for use when pressure is reduced upon the stored fuel to substantially atmospheric pressure.
Still another object of the present invention is to provide an improved method for the operation of internal combustion engine vehicles employing a gaseous hydrocarbon as the motive fuel.
These and other objects as well as advantages of the present invention will become more apparent from the following detailed description being provided upon the preferred embodiments,